Claimed signal might be due instead to helium leaking into the photomultiplier tubes.

Enlarge/ Scientists with Italy's DAMA/LIBRA collaboration have been claiming to see a seasonal shift in "dark matter wind" for over 20 years. New results don't support that, and a new hypothesis might explain what the collaboration is really seeing.

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Over 20 years ago, a team running an underground experiment in Italy announced that it had detected evidence of dark matter—a claim the collaboration maintains to this day. But many physicists remain unconvinced that the signals detected were really due to dark matter, and outside experimental results have been mixed.

A new paper in Nature reporting on results of a different, complementary experiment found nothing to support the controversial claim. And a draft paper posted to the online arXiv proposes an alternative hypothesis for what the Italian collaboration might really be seeing in their data. But neither paper is sufficient to put the matter to rest once and for all.

Seeing the dark

Dark matter is a mysterious substance that physicists believe comprises around 27 percent of the Universe. (The ordinary matter we see everyday accounts for just four percent, with the remaining 69 percent due to the even more mysterious dark energy.) The most likely candidate for the source of dark matter is a class of particles known as weakly interacting massive particles (WIMPs), named because they rarely interact with ordinary matter.

There are numerous experiments around the world hunting for these elusive WIMPs, using several different methods. Their detectors are usually housed deep underground, the better to reduce interference from cosmic rays, which mimic a dark matter signature in the data.

The detectors house a target material (germanium, silicon crystals, or liquid xenon); whenever an incoming dark matter particle collides with the nucleus of an atom in the target material, there should be a recoil effect, producing tiny flash of light (a scintillation). If the dark matter particle manages to transfer sufficient energy in that collision, the flash will be strong enough to be detected.

A seasonal fluctuation

But WIMPs have proven to be extraordinarily difficult to detect. Despite the occasional tantalizing hint, only one of the many experiments has made the claim that it has succeeded: the DAMA/LIBRA experiment (Dark Matter/Large Sodium Iodide Bulk for Rare Process), housed deep underground in the Grand Sasso mountain in central Italy. The DAMA/LIBRA results are very much in dispute within the broader dark matter community.

The current best theoretical model posits that there is a "halo" of dark matter particles moving with the Sun around our galaxy. The Earth orbits the Sun within that halo. That means that for half of the year, the Earth moves with the direction of the Sun's motion around the galaxy; the other half, it moves in the other direction. That should produce an effect in the data similar to running into a dark matter wind. "In the summer we're moving into the wind, so you see a slightly faster motion towards you, and in the winter we are not moving into the wind as quickly, and so you see dark matter, on average, as slower," said Rutgers University physicist Matt Buckley.

So DAMA/LIBRA looks for an annual shift in the collision events picked up by their detectors over the courses of a year. In 1997, shortly after the experiment went live, they announced they had detected just such a modulation, and interpreted this as evidence for a WIMP with a mass of around 10 GeV (giga-electron volts). Just last year, the collaboration presented similar results from a six-year data collection run, following an upgrade to the experiment in 2010. But other physicists had strong doubts—not about the signal, which was unmistakable, but about whether it was truly caused by WIMPs.

Attempts at outside confirmation have produced mixed, and therefore inconclusive, results.

Attempts at outside confirmation have produced mixed, and therefore inconclusive, results. Xenon10 (also located under the Gran Sasso mountain) and CDMSII (Cryogenic Dark Matter Search II in Soudan, Minnesota) both failed to detect a signal in that energy range, although both were sufficiently sensitive that they should have if DAMA/LIBRA really had detected dark matter.

Another experiment, CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) did find a faint signal, but it wasn't entirely consistent with DAMA/LIBRA's signal. And in 2011, an experiment called CoGeNT, designed specifically to disprove the DAMA claims, backfired when preliminary results appeared to confirm the finding instead. It was just a hint of a signal, and it disappeared with more data. But it kept the debate alive, and the arguments often got acrimonious. "You'd give a talk about dark matter and end up getting into fights with people," Buckley told Quanta in 2013.

Then, in 2017, the upgraded XENON100 experiment—considered to be among the most promising for confirming or disproving the DAMA/LIBRA claims—also failed to find any evidence for that signal. But DAMA uses a sodium iodide detector, while XENON100 uses (wait for it...) xenon. It’s possible that dark matter could interact differently with different materials, so physicists have been waiting for experimental results that also use a sodium-iodide detector. That's where COSINE-100 comes in.

Enlarge/ A physicist works on the DAMA/LIBRA experiment under Grand Sasso mountain in central Italy.

DAMA/LIBRA collaboration/LNGS-INFN

Housed deep underground in South Korea, COSINE-100 also uses detectors made of sodium iodide crystals, and is large and sensitive enough to hunt for the same dark matter signal supposedly detected by DAMA/LIBRA. The team analyzed data from the first 59.5 days of operation, and published their findings in December in Nature.

The results: "We didn't find dark matter, and we discovered that the DAMA/LIBRA measurements aren't consistent with the standard model for the dark matter halo," said co-author Nelson Carlin Filho of the University of Sao Paulo in Brazil. "We're not saying the researchers at DAMA/LIBRA were wrong. They may have captured a periodic modulation in actual signals. However, unless the dark matter model is significantly modified, the signals are highly unlikely to be attributed to interactions with WIMPs." The collaboration will need several more years of data before COSINE-100 can fully confirm or refute DAMA/LIBRA's claims.

The two experiments aren't entirely identical, however. While both experiments use the same target material, the crystals used by COSINE are a bit "dirtier," according to Buckley—that is, they weren't purified of radioactive isotopes to quite the same extent as the crystals used by DAMA/LIBRA. "It's not like COSINE has some really crappy crystal—it's just that it's very hard to make them pure," he said. "The levels here are incredibly small"—so small that if the equipment used in such experiments flies on an airplane, thus being exposed to more cosmic rays, the target will have measurably more radioactivity, even after five years.

In addition, DAMA is measuring a modulation in the dark matter wind, but COSINE is looking for an absolute rate for how fast it's moving—mostly because their "dirtier" crystals makes it more difficult to accurately measure the modulation. That's an important distinction. "To directly compare the two you need to know how fast the dark matter is moving," said Buckley. "If you make the standard assumption about [the conventional dark matter halo model], then these results rule out DAMA. But you could imagine that the dark matter is moving in a fundamentally different way."

Enlarge/ The COSINE-100 detector is housed within a nested arrangement of shielding components, as indicated by different colors.

COSINE-100 collaboration

University of Chicago physicist Juan Collar wasn't particularly impressed with the new paper from the COSINE-100 experiment and thinks it has limited relevance, mostly because he believes it is premature. "I think it is a bit of a publicity stunt on their side," he said. For instance, "The uncertainty they are assigning to their background models is very small. As someone who does these simulations for a living, I do not buy it."

That said, he does think this new paper is a harbinger of something much more interesting down the line. "What is really impressive is that they have almost matched DAMA's level of background at low energy," said Collar. "That is a first, and a remarkable achievement. What it means is that they will soon have, with certainty, the ability to put this mystery to rest, by seeing or not seeing that pesky modulation, while using the same target material. So the best from COSINE is still to come."

Blame it on helium

So if DAMA/LIBRA's signal isn't due to the dark matter wind, what could be producing it? Daniel Ferenc, a physicist at University of California, Davis, has proposed an intriguing new hypothesis: helium that has seeped into the photomultiplier tubes used in the experiment's detectors. As explained by University College London physicist Jon Butterworth at the Cosmic Shambles blog, "It is well-established that there are seasonal changes in the underground density of helium, connected to changes in temperature and the water table. Helium is a tiny atom, horribly penetrative, and could get into the DAMA detectors and cause this effect." It's a draft paper posted to the arXiv, and not yet peer-reviewed, but it's piqued the interest of people like Butterworth.

Ferenc stumbled upon the seeds for this new hypothesis while designing new prototype detectors for a next generation of physics experiments. Most dark matter experiments use photomultiplier tubes, a technology that is around 80 years old. Great care is taken to ensure these tubes are protected from outside contamination, but Ferenc and his colleagues realized that helium was still leaking into the tubes over time.

"Every photomultiplier tube in the world has helium in it," he said. "This is something you cannot eliminate." And that's bad news for sensitive detection experiments like DAMA/LIBRA that only pick up a few weak events per year. Effects from trace amounts of helium must be accounted for in the analysis to make sure what's being detected is a genuine dark matter particle. Hunting for dark matter is often compared to looking for a needle in a field of haystacks. "All of a sudden you realize you have much more hay in your haystacks than you thought before," said Ferenc.

"It is precisely the sort of thinking that we should be doing about finding alternative explanations to the DAMA modulation."

When Ferenc et al. searched for the term "helium" in all of the DAMA/LIBRA collaboration's papers, they got zero hits—another red flag. Nor did they find any mention of how the experiment might have protected itself from helium. Because DAMA/LIBRA is housed in a mine, and hence prone to trace amounts of radon, the collaboration did include protection from radon contamination in their design. But radon is a much heavier gas than helium, with an atomic mass of 222, compared to helium's 4. [corrected] "The bottom line is, what works for radon, doesn't work for helium," said Ferenc. He also found out that there is a helium liquefying facility quite close to the experiment, adding more circumstantial evidence for his hypothesis.

Ferenc is a leading expert on photomultiplier tubes, so physicists like Collar are taking his hypothesis seriously—at least the argument concerning the signal creation mechanisms for DAMA/LIBRA. "I think the paper could be improved, but it is precisely representative of the sort of thinking that we should be doing about finding alternative explanations to the DAMA modulation," said Collar.

Plenty of other scientists have offered theoretical explanations for the DAMA/LIBRA signal, suggesting they are detecting neutrons or cosmic rays. But Ferenc points out that none of these alternative explanations can really be tested. He and his colleagues think the collaboration can test this latest hypothesis for themselves, simply by unplugging their 25 pairs of photomultiplier tubes and replugging them back into different places. If the detectors still pick up the same signal, that would be conclusive evidence that the signal is due to helium, not dark matter particles, according to Ferenc.

"They just have to replug 25 cables," he said. "In about half a year, they will know the answer. If they see the same variation like they are seeing now, then it means it is not dark matter."

"In the summer we're moving into the wind, so you see a slightly faster motion towards you, and in the winter we are not moving into the wind as quickly, and so you see dark matter, on average, as slower," said Rutgers University physicist Matt Buckley.

This reminds me, tangentially, of the search for the luminiferous ether and the experiments of Michelson-Morley.

Been in the belly of that Mountain like a 100 times using the highway tunnel that also has the laboratory entrance in it.Every time I wonder what the **** the researchers in there are up to.

That is the entrance to Laboratori Nazionali del Gran Sasso. The have a ton (well, many tons) of neutrino and dark matter experiments there. They also house OPERA, the experiment (in)famous for the faster-than-light neutrino thing.

As someone who also works with PMTs in experimental physics (I just described every single experimental physicist doing neutrino or dark matter physics), if this is indeed the cause, I think this is really not a good look for DAMA/LIBRA. Helium intrusion into PMTs is one of the first things you learn about in the field! I don't want to take anything away from the paper which seems to have rather sophisticated models for modelling the effects of helium intrusion; however, quantification of gas-intrusion afterpulsing in your PMTs is:

1. not the most difficult thing to do, and2. obviously crucial.

If DAMA/LIBRA missed that, oof.

Edit: Basically, it's well known that helium can diffuse through UV-transparent glasses like fused quartz, and that helium in PMTs cause afterpulsing, so it is something you must always quantify, and you must have some way to exclude the afterpulsing background in your data selection.

How strong is the consensus currently about the reality of dark matter?(I'm asking because this article emits absolutely no doubt about its existence)

That's been a problem, in my eyes, for quite some time. There are discrepancies between our current models and observation. Dark matter (and energy) were hypothesized as plausible explanations accounting for them. All well and good, except these have been portrayed, at times, as fact--especially troubling when the claim is as extraordinary as "I can't tell you what its properties are, and it's all but undetectable."

Contrast with the Higgs boson, which I recall being portrayed as "theorized, speculated, unproven, etc." while being sought after. No one saying the theoretical work was provably wrong... only that scientific rigor and objectivity should be applied. And there is definitely risk in treating something unproven, even if likely, as true... as it serves to close other avenues of thought and research.

Ahh back to the old "maybe DM is not real". Its real. Get over yourselves. If it were not real the universe would be wildly different than it is. All of these say its matter. (as in, something with mass) 1.Rotation rates of galactic objects. 2. Gravitational lensing. 3. Cosmic background radiation. 4. Galactic collision dynamics (more as well but I have work to do)

How strong is the consensus currently about the reality of dark matter?(I'm asking because this article emits absolutely no doubt about its existence)

The consensus in physics is strong, but it's obviously not 100% till you detect it. The reason for the consensus is that multiple independent types of evidence point not only towards dark matter, but also towards the same dark matter density.

- Astronomical observation of galaxies (velocity distributions and rotation curves)- Lensing studies of clusters- Velocity distribution of clusters- CMB Radiation- Structure formation simulations- Probably more I can't remember off the top of my head

In addition, we know that the simplest forms of MOND cannot work, because different galaxies (even of similar masses) deviate hugely from the average rotation curves or from the Tully–Fisher relation. That is easily explained by DM by simply stating that different galaxies obviously have somewhat different amounts of dark matter vs normal matter. (See: https://www.nature.com/articles/s41550- ... SgGg%3D%3D)

How strong is the consensus currently about the reality of dark matter?(I'm asking because this article emits absolutely no doubt about its existence)

Literally as strong as it could possibly be without direct observation.

We have loads of circumstantial evidence for its existence and no other explanations. From what I understand the biggest reasons why we believe in day matter is how galaxies behave and gravitational lensing. Galaxies spin at speeds that would require them to have much more mass than we can see. We can make predictions about where dark matter should be. When we look at the sky to verify the predictions, we see gravitational lensing from mass that is there, but there is nothing there besides the mass.

There are some fringe theories that try to explain it away, but AFAIK none can explain it all. Theories like Modified Newtonian Dynamics (MOND), Quantized Inertia (QI) try to explain the orbital dynamics, but don't do a good job of explaining away the rest of dark matter's phenomenon.

So, we're left with either this matter that is completely undetectable exists, or, there are 6 or 7 entirely new branches of physics that have been completely overlooked. These new branches, when added together look exactly as if there was a bunch of mass that we can't see.

A nice example on how science most times works. You have an idea, formulate a theory and design an experiment to prove or disprove the given theory. Then you publish your methods, data and conclusions, so others can think about it. They did and found weaknesses and failed to reproduce, so they started refining experiments to have a closer look. Over time this leads to an broadly accepted prove, disprove or refined theory. It is a long and iterative process. Of cause a success on the first try would always be nice, but rare in things you cannot easily touch and see. The whole process is not a weakness, but the strength of science. It's not about dogma, but continuous improvement.

One more time for those slow on the uptake- Dark matter exists but we don't know what it is. Thus the name Dark Matter (for lack of a better name). It's there, but it doesn't interact with electromagnetic spectrum. We can't see the wind, but we know it's there by how it affects what we do see. The universe wouldn't behave as does without this mysterious stuff. We have barely scratched the surface of understanding how the universe works.

Ahh back to the old "maybe DM is not real". Its real. Get over yourselves. If it were not real the universe would be wildly different than it is. All of these say its matter. (as in, something with mass) 1.Rotation rates of galactic objects. 2. Gravitational lensing. 3. Cosmic background radiation. 4. Galactic collision dynamics (more as well but I have work to do)

But we don't know how the real universe actually is, that's the problem.

While it is entirely possible that the universe is different than we think it is, that's not the way to bet. E.g. MOND could explain DM observations, but then we'd have to accept MOND (Modified Newtonian Dynamics). Personally my money's more on dark matter.

One more time for those slow on the uptake- something explained by the hypothetical properties of Dark matter exists but we don't know what it is. Thus the name Dark Matter (for lack of a better name). It's there, but it doesn't interact with electromagnetic spectrum. We can't see the wind, but we know it's there by how it affects what we do see. The universe wouldn't behave as does without this mysterious stuff. We have barely scratched the surface of understanding how the universe works.

One more time for those slow on the uptake- something explained by the hypothetical properties of Dark matter exists but we don't know what it is. Thus the name Dark Matter (for lack of a better name). It's there, but it doesn't interact with electromagnetic spectrum. We can't see the wind, but we know it's there by how it affects what we do see. The universe wouldn't behave as does without this mysterious stuff. We have barely scratched the surface of understanding how the universe works.

Fixed that for you.

Again, *something* is there. It exists. What it is is up to the 'hypothetical properties' to *explain* what it is. That is what science does. It explains observed phenomenon -what this stuff *does* is an observed phenomenon- using the laws of nature as we understand them. We have to understand things further before we can explain it.

Edit- People seem to get hung up on the words 'dark' and 'matter'. It's just what we call this stuff for lack of a better name. (Dark energy is an even worse name for it's corresponding phenomenon, but we won't go there today.)

Ahh back to the old "maybe DM is not real". Its real. Get over yourselves. If it were not real the universe would be wildly different than it is. All of these say its matter. (as in, something with mass) 1.Rotation rates of galactic objects. 2. Gravitational lensing. 3. Cosmic background radiation. 4. Galactic collision dynamics (more as well but I have work to do)

But we don't know how the real universe actually is, that's the problem.

While it is entirely possible that the universe is different than we think it is, that's not the way to bet. E.g. MOND could explain DM observations, but then we'd have to accept MOND (Modified Newtonian Dynamics). Personally my money's more on dark matter.

See also Bullet Nebula (aka Bullet Cluster).

I haven't seen a MOND theory that could explain all the DM observations.

"In the summer we're moving into the wind, so you see a slightly faster motion towards you, and in the winter we are not moving into the wind as quickly, and so you see dark matter, on average, as slower," said Rutgers University physicist Matt Buckley.

This reminds me, tangentially, of the search for the luminiferous ether and the experiments of Michelson-Morley.

A LOT of dark matter experiments and theories bring those quandaries to mind.

Ahh back to the old "maybe DM is not real". Its real. Get over yourselves. If it were not real the universe would be wildly different than it is. All of these say its matter. (as in, something with mass) 1.Rotation rates of galactic objects. 2. Gravitational lensing. 3. Cosmic background radiation. 4. Galactic collision dynamics (more as well but I have work to do)

But we don't know how the real universe actually is, that's the problem.

While it is entirely possible that the universe is different than we think it is, that's not the way to bet. E.g. MOND could explain DM observations, but then we'd have to accept MOND (Modified Newtonian Dynamics). Personally my money's more on dark matter.

See also Bullet Nebula (aka Bullet Cluster).

I haven't seen a MOND theory that could explain all the DM observations.

https://iopscience.iop.org/article/10.1088/1475-7516/2018/12/009/meta

As yet there are no observations to prove or disprove the theory but it predicts a stronger light deflection for very compact galaxies. It could one day be falsified or confirmed by such a measurement.

"All of a sudden you realize you have much more hay in your haystacks than you thought before," said Ferenc.

I dunno if that simile is quite apt. Given that they (apparently) got false hits, it's more like "All of a sudden, you realized that you have a lot more needles than you thought before, but you're looking for the CORRECT needle."

It also seems to me in the COSINE-100 experiment that there's an assumption that the presence of dark matter is uniform. They seem to expect X events in Y time when they announced, after less than two months, that the DAMA/LIBRA results were wrong. From the inferences about its nature and computer models of where it might be, I'd find that to be a potentially unfounded assumption. It could simply be that the earth hasn't passed through a "dense" enough region of dark matter in that time frame to get a hit.

Granted, I don't know that it's NOT a uniform thing around us, but then, there's nothing to suggest it is, either. So I wonder how they could have arrived at such a seemingly definitive conclusion in such a short amount of time. Could that be part of the reason about why the announcement is thought to have been premature?

In any event, the more we learn (or don't, as it happens) about dark matter, the more one sees how science works. It's not ideal all of the time, but, then, the evidence is tenuous at best, and folks have to follow the evidence, like it or not. That most do is the part folks need to focus on. My impression here is that the DAMA/LIBRA results aren't dead, but might be on life-support and that in the next few years, COSINE-100 will either vindicate it, or drive the final nail into the coffin about it's results.

Ahh back to the old "maybe DM is not real". Its real. Get over yourselves. If it were not real the universe would be wildly different than it is. All of these say its matter. (as in, something with mass) 1.Rotation rates of galactic objects. 2. Gravitational lensing. 3. Cosmic background radiation. 4. Galactic collision dynamics (more as well but I have work to do)

But we don't know how the real universe actually is, that's the problem.

While it is entirely possible that the universe is different than we think it is, that's not the way to bet. E.g. MOND could explain DM observations, but then we'd have to accept MOND (Modified Newtonian Dynamics). Personally my money's more on dark matter.

See also Bullet Nebula (aka Bullet Cluster).

I haven't seen a MOND theory that could explain all the DM observations.

https://iopscience.iop.org/article/10.1088/1475-7516/2018/12/009/meta

As yet there are no observations to prove or disprove the theory but it predicts a stronger light deflection for very compact galaxies. It could one day be falsified or confirmed by such a measurement.

"All of a sudden you realize you have much more hay in your haystacks than you thought before," said Ferenc.

I dunno if that simile is quite apt. Given that they (apparently) got false hits, it's more like "All of a sudden, you realized that you have a lot more needles than you thought before, but you're looking for the CORRECT needle."

It also seems to me in the COSINE-100 experiment that there's an assumption that the presence of dark matter is uniform. They seem to expect X events in Y time when they announced, after less than two months, that the DAMA/LIBRA results were wrong. From the inferences about its nature and computer models of where it might be, I'd find that to be a potentially unfounded assumption. It could simply be that the earth hasn't passed through a "dense" enough region of dark matter in that time frame to get a hit.

Granted, I don't know that it's NOT a uniform thing around us, but then, there's nothing to suggest it is, either. So I wonder how they could have arrived at such a seemingly definitive conclusion in such a short amount of time. Could that be part of the reason about why the announcement is thought to have been premature?

In any event, the more we learn (or don't, as it happens) about dark matter, the more one sees how science works. It's not ideal all of the time, but, then, the evidence is tenuous at best, and folks have to follow the evidence, like it or not. That most do is the part folks need to focus on. My impression here is that the DAMA/LIBRA results aren't dead, but might be on life-support and that in the next few years, COSINE-100 will either vindicate it, or drive the final nail into the coffin about it's results.

DAMA results are incompatible with the kind of inhomogeneity you're describe anyway. To most physicists DAMA/LIBRA results are long dead.

He and his colleagues think the collaboration can test this latest hypothesis for themselves, simply by unplugging their 25 pairs of photomultiplier tubes and replugging them back into different places. If the detectors still pick up the same signal, that would be conclusive evidence that the signal is due to helium, not dark matter particles, according to Ferenc.

"They just have to replug 25 cables," he said. "In about half a year, they will know the answer. If they see the same variation like they are seeing now, then it means it is not dark matter."

Ummm, what? Could we get some detail on what moving the cable around would do? What is that going to tell them? What's going to change?

By merely reconnecting 25 out of the 50 signal cables from the PMTs, one can establish pairwise coincidences of PMTs that are optically coupled to different scintillators, instead ofthe same scintillators (alternatively, one can introduce delay lines). That way, the DAMA detector will become blind to the DM-like scintillation events, while it will remain equally sensitive to TheHeap events.

Although if someone could explain why the rewiring only affects Dark Matter scintillation events, and not Thermionic electron-induced He-ion after pulsing (TheHeap) events, that would be great.

One more time for those slow on the uptake- something explained by the hypothetical properties of Dark matter exists but we don't know what it is. Thus the name Dark Matter (for lack of a better name). It's there, but it doesn't interact with electromagnetic spectrum. We can't see the wind, but we know it's there by how it affects what we do see. The universe wouldn't behave as does without this mysterious stuff. We have barely scratched the surface of understanding how the universe works.

Fixed that for you.

Again, *something* is there. It exists. What it is is up to the 'hypothetical properties' to *explain* what it is. That is what science does. It explains observed phenomenon -what this stuff *does* is an observed phenomenon- using the laws of nature as we understand them. We have to understand things further before we can explain it.

Edit- People seem to get hung up on the words 'dark' and 'matter'. It's just what we call this stuff for lack of a better name. (Dark energy is an even worse name for it's corresponding phenomenon, but we won't go there today.)

Nope.

You could make the same argument of "luminiferous aether" up until the Michelson-Morley experiment (which in some ways the DAMA/LIBRA experiment is analgous to.)

I'm not saying dark matter doesn't exist, but saying that it does in such absolute terms is almost the same error.

Ahh back to the old "maybe DM is not real". Its real. Get over yourselves. If it were not real the universe would be wildly different than it is. All of these say its matter. (as in, something with mass) 1.Rotation rates of galactic objects. 2. Gravitational lensing. 3. Cosmic background radiation. 4. Galactic collision dynamics (more as well but I have work to do)

But we don't know how the real universe actually is, that's the problem.

While it is entirely possible that the universe is different than we think it is, that's not the way to bet. E.g. MOND could explain DM observations, but then we'd have to accept MOND (Modified Newtonian Dynamics). Personally my money's more on dark matter.

See also Bullet Nebula (aka Bullet Cluster).

I haven't seen a MOND theory that could explain all the DM observations.

One more time for those slow on the uptake- something explained by the hypothetical properties of Dark matter exists but we don't know what it is. Thus the name Dark Matter (for lack of a better name). It's there, but it doesn't interact with electromagnetic spectrum. We can't see the wind, but we know it's there by how it affects what we do see. The universe wouldn't behave as does without this mysterious stuff. We have barely scratched the surface of understanding how the universe works.

Fixed that for you.

Again, *something* is there. It exists. What it is is up to the 'hypothetical properties' to *explain* what it is. That is what science does. It explains observed phenomenon -what this stuff *does* is an observed phenomenon- using the laws of nature as we understand them. We have to understand things further before we can explain it.

Edit- People seem to get hung up on the words 'dark' and 'matter'. It's just what we call this stuff for lack of a better name. (Dark energy is an even worse name for it's corresponding phenomenon, but we won't go there today.)

Nope.

You could make the same argument of "luminiferous aether" up until the Michelson-Morley experiment (which in some ways the DAMA/LIBRA experiment is analgous to.)

I'm not saying dark matter doesn't exist, but saying that it does in such absolute terms is almost the same error.

Heh. *Something* is causing the phenomenon. We see and can measure that something is happening that our contemporary physics can not yet explain. Are you saying what we see happening is not happening? You seem-as I noted- hung up on the words 'dark' and 'matter'.

Edit- It took a guy named Newton to finally explain a phenomenon that had perplexed mankind since the dawn of time. Gravity was the 'dark matter' of his time.

Is there any reason DAMA/LIBRA dropped the S from Sodium besides to force the acronym?

I’m also wondering exactly property of dark matter is making it so doggone difficult to detect; we’ve been able to detect neutrinos more definitely, and they’re...I wanna say massless? Correct me if I’m remembering wrong, please.